A gas turbine includes a compressor, a combustor, and a turbine. The compressor takes in air, compresses the air to increase its pressure, and directs the high-pressure air to the combustor.
In the combustor, fuel is sprayed into the high-pressure air to combust the fuel. High-temperature combustion gas generated by the combustion of the fuel is directed to the turbine, and this high-temperature combustion gas drives the turbine.
Because the turbine and the compressor rotate about the same rotation shaft, this driving of the turbine drives the compressor, causing the compressor to take in and compress air, as described above.
The gas turbine operating as above may suffer from combustion oscillations during combustion of the fuel, and such combustion oscillations have been a cause of noise and vibration during operation of the gas turbine.
In particular, recent gas turbines have reduced the NOx (nitrogen oxide) level in the exhaust gas from the standpoint of the impact on the environment during operation and often employ lean combustion of fuel to reduce the NOx level. However, because lean combustion tends to cause unstable combustion, combustion oscillations are likely to occur. In order to reduce the noise and vibration caused by the combustion oscillations, combustors have been provided with an acoustic liner for absorbing relatively high-frequency noise, which is made of, for example, a porous plate and a cover that covers the outside thereof; or an acoustic damper having a large resonance space for absorbing relatively low-frequency noise.
Because the volume of the resonance space in the acoustic liner for relatively high-frequency noise is small, there are few space limitations in the casing during installation.
In contrast, because the volume of the resonance space in the acoustic damper for relatively low-frequency noise is large, there are space limitations in the casing during installation. Conventionally, as shown in, for example, PTL 1, in a combustor having a bypass flow path for allowing air in the casing to be introduced into the combustion gas, an acoustic damper that utilizes the circumference of the bypass flow path is provided.
Furthermore, as shown in, for example, PTL 2, a combustor having no bypass flow path has been proposed, in which the acoustic damper is connected to the acoustic liner fitted around the combustor and in which an acoustic portion forming the resonance space of the acoustic damper is provided so as to extend in the axial direction or radial direction of the combustor.